Impression Materials PDF

IMPRESSION MATERIALS  DEFINITIONS: Impression: It is a negative reproduction of the teeth and surrounding oral structures. Impression material: It the material that used for making impression. It is inserted into the mouth in a plastic form then set Cast (Model): It is the positive reprod...

IMPRESSION MATERIALS  DEFINITIONS: Impression: It is a negative reproduction of the teeth and surrounding oral structures. Impression material: It the material that used for making impression. It is inserted into the mouth in a plastic form then set Cast (Model): It is the positive reproduction of the teeth and surrounding oral structure. Die:It is the model of single tooth  IDEAL REQUIREMENTS IMPRESSION MATERIAL 1. It should be accurate to produce fine details. 2. It should be biocompatible with oral environment. It should be not toxic or irritant to the oral tissues. 3. It should be easily manipulated without complicated equipment. 4. It should have suitable working time. 5. It should have suitable setting time. 6. It should have acceptable taste and odor to the patient. 7. It should accept addition and correction. 8. It should be easily disinfected without loss of its accuracy. 9. It should have good shelf life.  FACTORSAFFECTING ACCURACY OF IMPRESSION MATERIAL 1. Flow: The material should have sufficient flow to record all fine details. It should have sufficient viscosity to be contained in the tray. 2. Hydrophilicity:The material should be hydrophilic to wet the oral tissues easily. 3. Dimensional accuracy: The material should not show any dimensional changes during setting (neither expansion nor contraction).  FACTORSAFFECTING ACCURACY OF IMPRESSION MATERIAL 4. Adhesion to the tray: The impression material should adhere to the tray during its removal from the patient’s mouth. 5. Elasticity: The material should be elastic after setting to record the undercuts without distortion or fracture. 6. Dimensional stability: The material should not show any dimensional changes during its storage (the time between making the impression until pouring it at the dental laboratory). 7. Compatibility with model and die materials: The impression material should not react with the model and die material or affects its setting reaction.  TRAYS: Types: According to material: 1- Metallic 2- Plastic According to perforations: ▪ Perforated Perforations provide mechanical interlocking with the impression for good adhesion to the tray ▪ Non-Perforated: The impression sticks to the tray by itself or after adhesive application Types: According to Use: ▪ Stock tray Used for making primary impression ▪ Special tray Used of making Secondary impression  IMPRESSIONS: Primary Impression Secondary Impression Tray used Stock tray Special tray Impression material Low accurate High accuracy accuracy Cast obtained Primary cast Secondary cast Wash Technique: It involves using of two impression materials over each other. The first material has high viscosity to fulfill the bulk of the stock tray, while the second one has high flow to record the fine details CLASSIFICATION OF IMPRESSION MATERIALS: 1. According to setting mechanism: a) Reversible: They soften by heat and harden by cooling (physical reaction). e.g.: impression compound and agar.  CLASSIFICATION OF IMPRESSION MATERIALS: 1. According to setting mechanism: b) Irreversible: They set by a chemical reaction. e.g.: plaster impression material, zinc oxide-eugenol, alginate and elastomers.  CLASSIFICATION OF IMPRESSION MATERIALS: 2. According to behavior after setting: a) Non elastic (rigid) impression materials: When removed from undercut they fracture or deform. They used for completely edentulous patients. 2. According to behavior after setting: b) Elastic impression materials: They recovered after removal from undercut. They used for both dentulous and edentulous patients.  NON-ELASTIC IMPRESSION MATERIALS PLASTER IMPRESSION MATERIAL IMPRESSION COMPOUND ZINC OXIDE AND EUGENOL  NON-ELASTIC IMPRESSION MATERIALS Plaster Impression Compound Zinc oxide and Impression Eugenol Mode of Powder + water ✓ Sheets and cakes. 2 pastes of different supply ✓ Sticks (green stick colors compound).  NON-ELASTIC IMPRESSION MATERIALS Chemical Reaction Physical Reaction Chemical Reaction Flow High flow Low flow Good flow Dimension Good Bad Good al accuracy  Plaster Impression Impression Compound Zinc oxide and Eugenol Adhere to tray Adhere to the tray Adhere to tray Adhere to the tray Elasticity Rigid. Rigid. Rigid. Dimensiona stability Good Bad Good Dimensional accuracy Good Bad Good Non-perforated acrylic Non-perforated stock tray. Non-perforated acrylic used Tray resin special tray. resin special tray. Uses Secondary impression Sheets and cakes: Secondary impression for ▪ Primary impression of for completel completely edentulous patients. completely y edentulous patients ▪ Tray material for wash technique edentulous patients (historically) (after border molding with zinc oxide-eugenol. with green stick Stick:Border molding (border tracing). compound)  Manipulation: 1. Plaster impression:Like Gypsum products Manipulation: Impression compound: Sheets and cakes: ▪ Heated in a water path (55 – 60 °C). ▪ Due to its lower thermal conductivity it should be immersed for sufficient time and kneaded. ▪ The material is kneaded outside the water to avoid water incorporation which acts as a plasticizer and increase the flow.  Manipulation: Impression compound: The sticks: They heated over a direct flame. ▪ Avoid overheating as it will cause volatilization of some ingredients which will affect its properties. Manipulation: 3. Zinc oxide and eugenol: ▪ Dispense equal lengths form both tubes on a glass slab or oil resistance pad. ▪ Mix using stainless steel spatula until homogenous color is obtained. ▪ Reaction is accelerated by: 1- Heat 2- Humidity. 3- Primary alcohols as Ethyl alcohol.  ELASTIC IMPRESSION MATERIALS HYDROCOLLOIDS ELASTOMERS  MIXTURES True solutions Colloids Suspensions Homogeneous mixture. Heterogeneous solution Heterogeneous mixture. e.g.: Sugar in water e.g.: Sand in water  Elastic impression materials are removed from patient’s mouth with sharp snap movement to:Increase tear strength. 2.Decrease permanent deformation. Synersis: a) Synersis and imbibition: It is the loss of the water. This occurs if the impression is left in the air. This results in shrinkage of the impression.  Imbibition: It is the uptake of the water. This occurs if the impression is immersed in water. This results in expansion of the impression. To avoid synersis and imbibition, the hydrocolloids impression should be stored in 100% relative humidity or stored in 2% potassium sulfate solution. b) Thermal changes: - In alginate impression, slight contraction occurs due to transfer of the impression from the mouth (37 °C) to room temperature (23 °C). - In agar impression, slight expansion occurs due to the difference in temperature of the water cooled tray (15 °C) to room temperature (23 °C). Hydrocolloids should be poured within short time. Hydrocolloids are non-toxic and non-irritant  Reversible hydrocolloid Irreversible hydrocolloid Agar impression material Alginate impression material Mode of Gel Powder + Water supply HYDROCOLLOIDS suppled in tubes and syringes. Tray Specially designed water cooled Perforated stock tray required perforated tray Alginate impression material The setting time of alginate can be managed by: 1. Water temperature (18 - 24°C). ▪ Increase water temperature will accelerate the reaction. ▪ This can be recommended way 2. Water/powder ratio: ▪ Increase water will retard the setting reaction. ▪ This is not recommended as it will adversely affect the properties of the material. Alginate powder should be stored under cool and dry conditions  Type of Setting Full Partial Crown, Study Impression Elasticity Process reaction Hydrophilicity Denture Denture or bridge Models Material Reversible hydrocolloid Elastic Physical reversible Hydrophilic Not used Yes Yes No (agar) Irreversible hydrocolloid Elastic Chemical Irreversible Hydrophilic Primary Yes No Yes (alginate) ELASTIC IMPRESSION MATERIALS HYDROCOLLOIDS ELASTOMERS  ELASTOMERIC IMPRESSION MATERIALS They are a variety of rubber-like impression materials that have several names as: ✓ Non-aqueous elastomeric impression materials. ✓ Rubber base materials. ✓ Elastomers. They set by a polymerization reaction. They supplied in different consistencies; light, medium, heavy and putty consistencies. They supplied in two containers; base and catalyst with two different colors. They have higher dimensional accuracy and stability than hydrocolloids. Elastomers are more expensive than alginate. ELASTOMERIC IMPRESSION MATERIALS  Type of Crown, Setting Full Partial Study Impression ELASTOMERIC IMPRESSION Elasticity reaction MATERIALS Hydrophilicity or Process Denture Denture Models Material bridge Polysulfide Elastic Polysulfide Chemical Condensation Irreversible Hydrophobic Addition Final YesPolyether Yes No (Mercaptan) silicon silicon (PVS) Condensation Elastic Consistencies Chemical Irreversible Light, Light, medium Hydrophobic medium, heavyFinal and Yes Yes Light, medium No silicone and heavy putty and heavy Addition Hydrophobic Elastic Chemical Irreversible Final Yes Yes No silicone Hydrophilic Polyether Elastic Chemical Irreversible Hydrophilic Final Yes Yes No Making secondary impression for dentulous and edentulous patients. Uses